Gastric or gastroesophageal junction (GEJ) adenocarcinoma remains a fatal condition worldwide, ranking fifth in prevalence and fourth in mortality globally [1]. The treatment of advanced gastric cancer is currently stratified based on MSI (Microsatellite Instability) status and HER2 status. For MSI-H (Microsatellite Instability-High) patients, clinical studies have shown that PD-1 inhibitor, either as monotherapy [2] or in combination with CTLA-4 inhibitor [3], offer significant therapeutic benefits. For HER2-positive patients, the results from the KEYNOTE-811 study [4] have established a standard treatment regimen that includes chemotherapy combined with immunotherapy and anti-HER2 targeted therapy. For HER2-negative patients, based on the results of clinical trials including ATTRACTION-4 [5,6], CheckMate-649 [3,7,8], COMPASSION-04 [9], KEYNOTE-062 [2], KEYNOTE-859 [10], ORIENT-16 [11] and RATIONALE-305 [12], immune checkpoint inhibition (ICI) combined with chemotherapy has become the standard first-line treatment. These clinical studies compared the clinical efficacy of chemotherapy combined with immunotherapy to that of chemotherapy alone (Table 1). As shown in these studies, patients with advanced gastric cancer exhibited an objective response rate (ORR) of approximately 47%-60%, a median progression-free survival (mPFS) ranging from 6.9 to 10.45 months, and a median overall survival (mOS) between 12.9 and 17.45 months following the combination of chemotherapy and immunotherapy. These therapeutic outcomes demonstrate significant benefits over chemotherapy alone. Clinical and preclinical studies have suggested that immunotherapy may activate T cells in gastric cancer patients, thereby enhancing treatment efficacy. Optimizing the immune microenvironment or selecting patients more likely to benefit from immunotherapy could potentially improve outcomes. It is important to note that the benefit from combined chemotherapy and immunotherapy is primarily seen in patients with a PD-L1 CPS (Combined Positive Score) of ≥5. Patients with a CPS <5 do not exhibit significant clinical benefits. Additionally, the benefit of immunotherapy combined with chemotherapy remains controversial for patients with peritoneal metastasis [5]. Thus, enhancing the efficacy of treatments for advanced gastric cancer patients remains an urgent area of research. Adding anti-angiogenic therapy to chemoimmunotherapy appears to be a promising strategy to enhance the efficacy of ICI. Currently, two major categories of anti-angiogenic agents are widely used in clinical practice: antibodies and TKIs (tyrosine kinase inhibitors). These agents primarily function by blocking the VEGFA-VEGFR2 axis, which leads to the normalization of tumor vasculature [13]. This process corrects abnormal vascular structures such as excessive tortuosity and coiling [14], increases the formation of high endothelial venules (HEVs) [15], pericytes, and vascular basement membranes [16]. Thus, this normalization process alleviates the hypoxia, low pH, and immunosuppressive characteristics of the tumor microenvironment (TME) [17]. This normalization enhances the infiltration of active T cells and reduces the infiltration of immunosuppressive cells, such as tumor-associated macrophages and myeloid-derived suppressor cells, ultimately improving the efficacy of ICIs [18]. Notably, in the treatment of various tumors, including gastric cancer, it has been observed that combining immunotherapy with anti-angiogenic therapy has a synergistic effect in later-line treatments [19,20].

Consequently, our research group conducted the SPACE trial in June 2020 [21], with findings published in Signal Transduction and Targeted Therapy (STTT) in March 2024. The primary endpoints of this single-arm Phase 1 clinical trial are the maximum tolerated dose (MTD) and ORR. The study aims to increase the ORR from 50% to 70% by adding the anti-angiogenic agent apatinib to the combination of chemotherapy (SOX regimen) and immune checkpoint inhibitor (camrelizumab). As this is the first-time chemotherapy, immunotherapy, and anti-angiogenic therapy have been combined, the study is designed with a Phase Ia dose-escalation phase with three dose levels (Dose regimen 1: camrelizumab 200 mg on day 1, apatinib 250 mg every other day, oxaliplatin 100 mg/m² on day 1, and S-1 40 mg twice a day on days 1–14. Dose regimen 2: same as dose regimen 1, but oxaliplatin 130 mg/m². Dose regimen 3: same as dose regimen 2, but apatinib 250 mg daily), followed by a dose-expansion phase (Phase Ib) to select the optimal dose group. A total of 34 patients were enrolled in the study, with 9 patients in the dose-escalation phase (3 patients each at dose 1, 2 and 3) and 26 patients in the dose-expansion phase. Among these patients, 22 (64.7%) had metastases in two or more organs, 19 (55.9%) had poorly differentiated histology, 30 (88.2%) were microsatellite stable (MSS), 19 (55.9%) had low tumor mutation burden (TMB), and 17 (50.9%) had a CPS <1, indicating a generally poor baseline condition. Despite this, in the full analysis set, 26 patients achieved partial response (PR), 5 patients had stable disease (SD), and only 2 had progressive disease (PD), resulting in a confirmed ORR of 76.5% (95% CI 58.8–89.3) and a disease control rate (DCR) of 91.2% (95% CI 76.3–98.1), which is significantly better than the results of chemoimmunotherapy. In terms of prognosis, in the full analysis set, 14 patients experienced PD or death, with an mPFS of 8.4 months (95% CI 5.9-NE); 12 patients experienced death, and the mOS has not yet been reached, the 1-year and 2-year OS rates were 69.1% (95% CI 49.9–82.2) and 62.8% (95% CI 41.3–78.3), respectively. Among the 10 patients who underwent curative gastric cancer surgery, 9 (90%) achieved R0 resection, 3 (30%) achieved pathological complete responses (pCR), and 5 (50%) achieved major pathological responses (MPR), suggesting the potential value of this triple therapy in conversion therapy. In the 24 patients who did not undergo surgery, the mOS reached 19.6 months, which is notably better than the data for chemoimmunotherapy.

Further subgroup analysis revealed that even among patients with a combined positive score (CPS) <1 (N=17), the ORR reached 70.6% (95% CI 44.0–89.7), which is significantly better than the data for chemoimmunotherapy. In the CPS ≥ 1 (N=12) subgroup, the ORR reached 91.7% (61.5–99.8), and in the CPS ≥ 5 (N=7) subgroup, the ORR achieved 100%. As for the safety analysis set of SPACE, all patients experienced treatment-emergent adverse events (TEAEs) of any grade, 18 patients (52.9%) encountered grade 3 or higher TEAEs, and 5 patients (14.7%) experienced grade 3 or higher immune-related adverse events (irAEs). Only one patient died due to gastrointestinal causes, showing the adverse reactions were within manageable levels. In the ORIENT-16 study, the incidence of grade 3 or higher adverse events in the chemotherapy plus immunotherapy group was 59.8%. Similarly, in the RATIONALE-305 study, the incidence of grade 3 or higher adverse events was 54%. Therefore, it appears that adding anti-angiogenic therapy did not significantly increase the occurrence of severe adverse events. In conclusion, camrelizumab plus apatinib and chemotherapy showed favorable clinical outcomes and manageable safety for untreated advanced gastric cancer. It is important to note that the follow-up of OS, the most reliable measure of anti-tumor efficacy, is crucial. Indeed, a favorable ORR does not necessarily translate into improved OS outcomes, so we will continue follow-up and conduct larger clinical studies to verify the OS benefits of the triple therapy. Beside the SPACE study, to our knowledge, there is only one clinical study published that focus on first-line treatment combining chemotherapy, immunotherapy, and anti-angiogenesis for unresectable advanced gastric cancer which was launched in February 2021. NCT04757363 [22], a single-arm, phase 2 trial conducted at Memorial Sloan Kettering Cancer Center (MSKCC) in the United States, involved 39 patients with advanced metastatic gastric cancer. They were treated with chemotherapy (FOLFOX), immunotherapy (nivolumab), and anti-angiogenic agent (regorafenib). Among them, 29 patients (83%) had distant metastases, 30 patients (86%) had metastases in two or more organs, 16 patients (46%) had signet ring cell carcinoma, 20 patients (57%) had a CPS <1, and 34 patients (97%) were microsatellite stable, indicating similar challenging baseline characteristics compared to our trial. In the full analysis set, 22 patients (76%) achieved an objective response, including 3 complete responses (10%) and 19 partial responses (66%). The 6-month and 12-month PFS rates were 71% (95% CI 54–85) and 51% (95% CI 37–71), respectively. The 6-month and 12-month OS rates were 97% (95% CI 92-100) and 85% (95% CI 74-98), respectively. Researchers further conducted an analysis on a subgroup of 20 patients with CPS <1, finding an ORR of 75% and a 6-month PFS rate of 75%. As for the safety analysis set of this trial, 97% of the patients experienced TEAEs of any grade, 59% encountered grade 3 TEAEs, and 18% experienced grade 4 TEAEs, which is slightly more severe compared to the SPACE study. In conclusion, this study further demonstrated the efficacy and manageable safety of chemotherapy combined with immunotherapy and anti-angiogenesis treatment in advanced gastric cancer. Certainly, both our SPACE study and the trial from MSKCC are small-sample Phase 1-2 clinical trials, and the level of evidence is still relatively low. By comparing these two studies, we found that the clinical research from MSKCC seems to have achieved better outcomes than our SPACE study. We speculate the primary reason may be that regorafenib is a multi-target TKI. At clinical doses, regorafenib and its metabolites inhibit a wide range of kinases, including RET, VEGFR1, VEGFR2, VEGFR3, KIT, PDGFR-α, PDGFR-β, FGFR1, FGFR2, TIE2, DDR2, TrkA, Eph2A, RAF-1, BRAF, BRAFV600E, SAPK2, PTK5, Abl, and CSF1R [23]. In contrast, apatinib is a single-target TKI that primarily inhibits VEGFR2 at clinical doses. This suggests that using a multi-target TKI in combination therapy may offer superior efficacy. As a result, large-scale Phase 3 randomized controlled trials are needed to further confirm whether the addition of anti-angiogenic drugs to chemoimmunotherapy can improve the ORR and extend OS. Just as chemotherapy combined with immunotherapy became the first-line treatment for advanced gastric cancer in the Chinese Society of Clinical Oncology (CSCO) guidelines in 2024, the success of numerous clinical studies on the combination of chemotherapy, immunotherapy, and anti-angiogenic therapy suggests that the triple therapy is likely to become a standard clinical practice for treating advanced gastric cancer in the future. In traditional immunotherapy combined with chemotherapy, PD-L1-negative patients often exhibit limited efficacy. However, in the SPACE trial, anti-angiogenic therapy significantly enhanced the therapeutic outcomes in PD-L1-negative patients. Even among patients with CPS <1, the ORR reached 70.6%. Similar conclusions were drawn from the NCT04757363 trial [22]. This may be attributed to the increased tumor microenvironment PD-L1 expression induced by anti-angiogenic agents. Shigeta et al. [24]. confirmed in a preclinical mouse model of hepatocellular carcinoma that blockade of VEGF2 led to elevated PD-L1 expression in tumor cells, and compared to monotherapy, the combination of immunotherapy with anti-angiogenic treatment significantly improved efficacy. It is also important to recognize that the dosage of anti-angiogenic agents plays a crucial role in determining the outcome of therapy. The dose-response relationship for these drugs is not straightforwardly linear; excessively high doses not only increase the incidence of adverse reactions but can also cause excessive pruning of tumor vessels [25]. This excessive pruning may lead to insufficient tumor perfusion, exacerbate the tumor’s hypoxic microenvironment, and ultimately foster tumor progression [25]. Preclinical studies in mouse models of breast cancer have demonstrated that, compared to higher doses, lower doses of anti-VEGFR2 antibodies result in a more evenly distributed and functional tumor vasculature, which improves tumor control [26]. In our SPACE trial, the established dose for apatinib was set at 250 mg/day, administered continuously over a 21-day cycle, which is a relatively small dose compared to the single agent recommendation in third line treatment [27,28]. Surprisingly, among the 6 patients receiving 250 mg every other day of apatinib, 5 patients with efficacy evaluation data achieved a 100% ORR. It can be speculated that even a low dose of apatinib appears to exhibit significant efficacy. Therefore, it is necessary for future large-scale clinical studies to include different dosage gradients of anti-angiogenic drugs. This will allow for a comparison of efficacy and safety, helping to determine the optimal dosage of anti-angiogenesis drugs for combination therapy.

Other than unresectable advanced gastric cancer, the chemotherapy-immune-antiangiogenic triple therapy has also become a significant research focus for the treatment of potentially resectable locally advanced gastric cancer. The LAGC trial [29], a multicenter, randomized, controlled phase II study conducted in Fujian, China, included 106 patients with T2-4N+M0 potentially resectable locally advanced gastric cancer. Participants were randomly assigned to either the CA-SAP group (chemotherapy with albumin-bound paclitaxel plus S-1, immunotherapy with camrelizumab, and antiangiogenic therapy with apatinib) or the SAP group (chemotherapy with albumin-bound paclitaxel plus S-1). The primary endpoint was the major pathologic response (MPR). The results demonstrated that the MPR rate in the CA-SAP group was significantly higher than in the SAP group (33.3% vs. 17.0%, P = 0.044). Additionally, the CA-SAP group showed a significantly higher ORR (66.0% vs. 43.4%, P = 0.017) and R0 resection rate (94.1% vs. 81.1%, P = 0.042) compared to the SAP group. The DRAGON IV trial [30], a multicenter, randomized, controlled phase III study conducted in China, enrolled 360 patients with T3-4aN+M0 potentially resectable locally advanced gastric cancer. Participants were randomly assigned to the SOXRC group (chemotherapy with SOX, immunotherapy with camrelizumab, and antiangiogenic therapy with apatinib) or the SOX group. The primary endpoint was the pCR rate. The results showed a statistically significant improvement in pCR assessed by BIRC for the SOXRC group (18.3%, 95% CI 13.0-24.8) compared to the SOX group (5.0%, 95% CI 2.3-9.3), with an improvement of 13.7% (95% CI 7.2-20.1, P <0.0001). The MPR rates were 51.1% for the SOXRC group and 37.8% for the SOX group. These findings highlight the potential benefits of incorporating immunotherapy and antiangiogenic therapy into the standard chemotherapy regimen for patients with potentially resectable locally advanced gastric cancer.

Beyond gastric cancer, various other types of cancer have seen a surge in clinical studies focusing on the integration of chemotherapy, immunotherapy and anti-angiogenic therapies. In the field of extensive-stage small cell lung cancer (ES-SCLC), the ETER701 study [31] is a multicenter, double-blind, randomized, placebo-controlled Phase 3 trial investigating the efficacy and safety of chemotherapy combined with benmelstobart (a PD-L1 inhibitor) and anlotinib (a multi-targeted TKI). The results demonstrated that the combination of chemotherapy with the PD-L1 inhibitor and anlotinib (n=246) resulted in a significantly longer mPFS [6.9 months (95% CI 6.2–8.3) versus 4.2 months (95% CI 4.17–4.24); HR 0.32 (95% CI 0.26–0.41); P < 0.0001] and mOS [19.3 months (95% CI 14.2 to not estimable) vs. 11.9 months (95% CI 10.7–13.4); HR 0.61 (95% CI 0.47–0.79); P = 0.0002] compared to the chemotherapy-alone group (n=247), while also showing manageable safety. In the field of non-small cell lung cancer (NSCLC), the IMpower150 study [32], which is a pivotal international multicenter randomized controlled Phase 3 trial, involved 1,202 treatment-naïve patients with advanced NSCLC who were randomized to receive atezolizumab plus carboplatin and paclitaxel (ACP group), bevacizumab plus carboplatin and paclitaxel (BCP group), or a combination of atezolizumab, bevacizumab, carboplatin, and paclitaxel (ABCP group). Subgroup analyses of the ACP and ABCP groups based on KRAS mutation status revealed that patients with KRAS mutations exhibited significantly longer mOS and mPFS in the ABCP group compared to the ACP group (mOS: 19.8 vs. 11.7 months; mPFS: 8.1 vs. 4.8 months). The APPLE trial [33], another notable study recently conducted in Japan, randomized 412 treatment-naïve advanced NSCLC patients to receive atezolizumab plus carboplatin and pemetrexed (APP group) or atezolizumab, carboplatin, pemetrexed, and bevacizumab (APPB group). The researchers found that the APPB group showed a more pronounced benefit over the APP group in terms of mPFS (9.7 vs. 5.8 months) in patients with driver gene mutations. In the field of potentially resectable esophageal cancer, 42 patients receiving chemotherapy (nedaplatin and albumin-bound paclitaxel), immunotherapy (camrelizumab), and anti-angiogenic therapy (apatinib) achieved a 100% disease control rate (DCR) and an 83.3% ORR [34]. In the field of advanced biliary tract cancer, the SAGC study [35] is the first randomized controlled Phase 2 trial investigating the efficacy of a first-line treatment regimen combining chemotherapy (GemCis), immunotherapy (sintilimab), and anti-angiogenic therapy (anlotinib). The study included 48 patients, with 26 receiving the triple therapy and 22 receiving chemotherapy alone. The results showed that patients receiving the triple therapy had a longer mPFS compared to those receiving chemotherapy alone (6.4 vs. 5 months; p=0.014). In the field of advanced colorectal cancer, the AtezoTRIBE study is a multicenter, open-label, randomized, controlled Phase 2 trial evaluating the efficacy and safety of chemotherapy (FOLFOXIRI regimen), immunotherapy (atezolizumab), and anti-angiogenic therapy (bevacizumab) in patients with advanced metastatic colorectal cancer. The results indicated that the combination of FOLFOXIRI, atezolizumab, and bevacizumab provided an mPFS benefit compared to FOLFOXIRI combined with bevacizumab alone (13.1 vs. 11.5 months, p=0.012), but there was no significant benefit in OS (33 vs. 27.2 months, P=0.136) [36,37]. Aside from a few Phase 3 clinical trials, most of the studies have been small-sample Phase 2 trials. Therefore, there is a general lack of comparative studies, particularly high-quality Phase 3 trials, to further confirm the efficacy of these combination therapies. Additionally, it is important to note that not all studies involving combination therapies with anti-angiogenic agents yield positive results. In the IMbrave151 study for advanced biliary tract cancer, the combination of chemotherapy with bevacizumab and atezolizumab did not show better mPFS compared to the combination of chemotherapy and atezolizumab alone (8.3 vs. 7.9 months, HR = 0.76 [0.51–1.14]). The CheckMate 9X8 study [38], another multicenter, open-label, randomized, Phase 2/3 trial, evaluated the efficacy and safety of a triple therapy regimen comprising chemotherapy (standard of care regimen), immunotherapy (nivolumab), and anti-angiogenic therapy (bevacizumab) in advanced colorectal cancer. However, compared to the chemotherapy and anti-angiogenic therapy group, the triple therapy did not provide an mPFS benefit [11.9 vs. 11.9 months, HR 0.81 (95% CI, 0.53 to 1.23); p=0.30], despite a higher ORR (60% vs. 46%).

In first-line treatment, there are two main categories of anti-angiogenic agents used in combination with immunotherapy: Small Molecule VEGF TKIs and monoclonal antibodies. VEGF TKIs include apatinib, fruquintinib, anlotinib, lenvatinib, regorafenib, and sorafenib. VEGF TKIs primarily work by inhibiting the VEGF receptor (VEGFR) tyrosine kinase, thereby blocking the signaling pathways that promote tumor angiogenesis and endothelial cell proliferation. As for monoclonal antibodies, the most common example is bevacizumab. Bevacizumab works by directly binding to VEGFA, preventing it from interacting with VEGFR on endothelial cells, which in turn inhibits the formation of new blood vessels necessary for tumor growth. Both categories of drugs are currently being investigated in clinical studies, with several successful examples. However, it remains unknown which type of drug is more effective in improving the immune microenvironment and synergizing with immunotherapy. The effectiveness of these agents may vary depending on the type of cancer and the sensitivity of tumor cells to these drugs. Existing research suggests that there may be more studies focusing on the combination of immunotherapy with small molecule VEGF TKIs. This might be related to the off-target effects of TKIs. Besides selectively targeting VEGFR, many VEGF TKIs also interact with other tyrosine kinases, such as RET, TYRO3, AXL, and MERTK. These kinases are highly expressed on immune cells and blocking them may reduce the infiltration of myeloid-derived suppressor cells and activate T cells, potentially enhancing the efficacy of immunotherapy [25]. To extend our understanding, we summarized clinical trials initiated in 2024 involving the triplet therapy by searching the ClinicalTrials.gov Registry and Chinese Clinical Trial (Table 2). As shown in the tables, triplet therapy has emerged as a significant focus of contemporary research, particularly in the realm of gastric cancer, colorectal cancer, hepatocellular carcinoma, biliary tract cancer and lung cancer.

In Summary, the SPACE trial serves as a prime example demonstrating remarkable advancements in the response of advanced gastric cancer by incorporating anti-angiogenic agents with chemotherapy and immunotherapy both in PD-L1-positive and PD-L1-negative patients. However, the impact on OS is still unclear. More and large sample prospective multicenter Phase 3 clinical trials focusing the survival data are needed to further validate the applicability of this triplet regimen in gastric cancer. Furthermore, the biomarker and dynamic tumor microenvironment study should be done to clarify the mechanism why the adding of anti-angiogenisis inhibitor would increase the efficacy. Additionally, in gastric cancer and other tumors, the types of anti-angiogenic agents to combine and the optimal dosing of these agents still need to be explored in different contexts. Lastly, since both SPACE study and the NCT04757363 trial showed potential efficacy in PD-L1 negative patients, triplet therapy could be tested in these patients in the future.